Process for working zinc



April 29, 1924.

W. M. TOWNE PROCESS FOR WORKING ZINC Filed Aug. 21, 1922 By Attorneys; @mu QM v M. TOWNE, F BROOKLYN, NEW YOEK,'.AB8IGNOB, BY DIRECT AND z- PATENT OFFIC ASSIGNMENTS, T0 E. W. BLISS COMPANY, 015' NEW YORK N. Y., A GOBEOTION 0 new roan.

YBOCEBS FOR WORKING ENG.

Application filed August 21, 1922. serial H0. 5833M.

To all whom it may concern: Be it known that',I, WALTER M. TowNn, a citizen of the United States of America,

residing in the borough of Brooklyn, county e ofKings,'city and State of New York, have invented certain new and useful Improvements' in Processes for Working Zinc, of

which the followin' is a specification. I

a This invention re ates to a method of makingfzinc tubular articles, especially those in the form of cups or containers. The invention provides means for forming such articles by extrusion.

' 'Heretofore such articles of zinc have been most commonly made by forming sections of tube and soldering to one end of each a disk. This is a' difficult soldering operation, and the articles thus made are unduly-' expensive. Another method which has been successfullypractised consists in cutting a: blank from sheet zinc' and drawing it. into cup form'be-.'

tween dies, the diameter being reduced'in successive stages, and the cup elongated to bring it to the required size and shape. For

a cylindrical cup with a length about twiceits diameter, usually 'foursuccessive drawing operations are required, necessitating four sets of dies and a corresponding .number of re-handlings of the articles; The present invention enables such cup-shaped articles;

one pair of dies and at so in course of production.

to be produced with one stroke.

According to the present invention, a suit- 9 eter not exceeding that of the cup to be madef and'of such thickness as to afford the requisite amount of metal. This blank is of soft zincof suitable purity and homogeneity. It is placed in the cavity of-a dieor 'matrix having parallel outer surfaces "corresponding in diameter and outline to the exterior dimensions of the cup or article to be formed. A male die or punch is prothe difierence in size agreeing with the desired thickness of the walls of the cup to be made. This punch being properly guidwalls of the cu being formed flow up alongably shaped blank is first formedofa diamvided of corresponding but smaller outline, made andin the thickness of its walls.

ment of the dies during extrusion.

annular space between them, so that the the punch, this operation-being continued '5 w th the descent of the punch until the'fcup' reaches the proper dimensions; that is "to' say, until the end of the unch approaches as closely to the bottom oi the cavity in the matrix as is desired to give'the bottom ofi W the cup' the proper thickness. The active portion of the punch is atits lowerend where the" metal flows from its bottom around its sides, and directly above this active portion the. unch is reduced or tapered back, so as to re ieve the flowing zinc (if-in ternal pressure and' friction lmmediately after its-extrusion. The operation is per-' formed'with the zinc at'a temperature close- 1y, approximating 150 (3. The accompanying drawings illustrate one embodiment. 'of the "invention, com rising dies for forming a cup-shaped artic e or cylindrical container.

Figure 1 is a vertical mid-section of the;

male die or punch.

' die or matrix.

Fig. 3 is an oblique elevation of the blank. Fig. .4 is a sectional view, showing the condition'iduring the early part of the 'extruding operation. Fig. 5 is a similar view, the unch being in elevation, showing the comp etion'of the operation.

i Referring to the drawings, A is the punch or male die and B the female die or matrix. The latter is formed with a cavity or hol-' low I), which'in plan is of'the-shape and dimensions of the exterior of the article to be formed (being circularv for a cylindrical article), and having a depth somewhat more" than sufiicient'to receive the thickness of the blank -jshown in Fig. 3.- This thickness will vary for a iven diameter with the variations-in the engthof the article to get T e inner walls of the matrix are formed perpendicular to the plane of the die,- that is parallel with the relative direction of move The bottom of the matrix is curved, flat or otherwise according to the shapeto be given to y the bottom of the article to be formed. The

' c of the punch is made fiat or curved according to the shape of the interior of the bottom of the cup or other article to be formed. If this bottom portion is to be of uniform thickness. the bottom 0 of the punch is made parallel with the bottom of the cavity in the matrix or die B. The punch is reduced in diameter directly above the active portion a by being tapered back so as to relieve the zinc of pressure as soon as the fiowing zinc has been conformed between the portions a b of the dies. The punch A is provided with a shank portion A of any suitable shape and construction to fit the corresponding member of the press in which the dies are to be used. In a ress of the usual construction the die B wi 1 be carried in a die block on the bedrof the press and the punch A will have its shank A centered and fastened in a bolster or other fitting fastened to the moving head or platen of the press. Usually the construction of such presses is sufiiciently close and accurate to guide the punch and die in proper relation and keep the punch properly centered with reference to the cavity in the die. In Fig. 1 the punch is shown as having within it a knock-out bar D enlarged at its lower end to form a head d which constitutes a portion of the bottom 0 of the punch. The bar D projects out through the top of the punch to a suitable height so that its upper end may be struck by a stop or operating lever in the manner well understood in presses of this kind. Preferably the'knock-out bar is held up by a spring 6 pressing upwardly against a collar 7.

In practising the process of this invention,

. it is desirable for the most successful results to conform to the following requirements:

The blank is to be made of soft zinc of such approximation to purity as will cause it to flow uniformly. Zinc having a scleroscopic (Shore test) hardness of not over 23 should be used in order that the proper working condition may be obtained through subjection to heat for a short time. The zinc should have a lead content not exceeding 0.6 per cent and a cadmium content not exceeding 0.5 per cent. It is preferable to use pack rolled zinc by reason ofits more favorable property as to grain due to rolling. Pack rolled zinc gives better results than strip-rolled zinc, which has a decided grain and has been found to be more ductile in direction with the grain than across the grain. For this reason when stri rolled zinc is used, the extruded cup runs high on diametrically opposite sides where the fiow is with the grain and low on the other two sides where the flow is across the grain, so that the extrusion leaves the. metal under unequal strain and more scrap has to be trimmed off, and it is more difficult to control the height of the extruded cup. The use of pack rolled zinc avoids these disadvantages, since it has a substantial absence of grain direction, and the extrusion affords substantially uniform strain around the cup and runs to a uniform height.

It is important that the zinc be worked at a temperature approximating as closely as possible to 150 C. This temperature gives suflicient plasticityand ductility to form a cup or tu c with a thin wall. For thicker walls or purer zinc a lower temperature is admissible; but the method finds its most advantageous use in making cups with thin walls, and using zinc with approximately the percentage of lead and cadmium above indicated. At lower temperatures the internal friction of the metal increases, and it becomes stiffer and more difficult to extrude. At hi her temperatures there is a decrease in its uctility. In practice the blank should be heated to a somewhat higher temperature to make allowance for the cooling of the blank whilebeing placed in the dies and for the heat taken up by the dies. The precise drop to be thus allowed for must be deter mined in each case by experiment.

The proper lubrication of the blank is practically important. The best lubricant thus far found is lard oil. ()nly suflicient lubricant should be used to form a very thin film on the blank; if more is applied, it is desirable to rub off the excess so as to leave the blank apparently clean. An excess of lubricant causes the metal to rupture in the forming of the cup or tube, and introduces difficulty in controlling the flow of the metal. If no lubricant or insufficient lubricant be used, the zinc is liable to flake in the dies, and the latter are subjected to excessive wear.

The final essential to successful extrusion is the exercise of precision in the reciprocal formation of the die surfaces and the extreme hardening of these surfaces. It has been found that zinc can be successfully extruded only when the dies are so conformed that an equal and uniform flow of the metal occurs from the beginning of the pressure to the finish of the extruding stroke. If because of faulty construction or conformation of the dies, the metal is allowed to become pocketed or retarded at any point, so

that its flow is not thus continuous, it will immediately stiffen and lose its plasticity. 1B or this reason the described construction I of the active faces of the die cavity and the punch, or some other conformation for obtaining the same result, must be provided. The lower outer edge a of the punch around which the extruding metal flows in begin ning its ascent along the outer wall of the die cavity should be formed with a sharply rounded corner. Directly above this corner the metal should be tapered back, so as to relieve its pressure against the inner face of the extruding metal so that the latter may flow as freely as possible after haying been shaped between the die surfaces, and whereby needless friction and consequent waste of power are avoided. For clearness this tapering back orreduction of the punch is'somewhat exaggerated in Figs. 4 and 5. It is to be understood that the diminution does not need to be suflicient to bring the outer face of the punch actually out of contact with the inner face of the flowing wall of metal, but need be only enough to diminish frictional adhesion, the amount of which in the drawing would be nearly imperceptible. The lower outer corner of the bottom of the die cavity should be very slightly rounded, being made as sharp as is mechanically possible.

It is important to have a suitable conformation between the bottom a of the punch and the bottom of the die cavity, in order not only to give the desired shape to the bottom of the cup to be formed, but what is more important, to cause the extruding metal to flow uniformly from the center outwardly to the annular space between the punch and matrix. The flow should be slowest at the center and should accelerate uniformly in radial lines toward the outer wall,

the maximum rate of flow being through the contracted annular space where the extrusion finally occurs.

Owing to the tendency of the zinc to hug or close in around the punch, it has been found advisable to remove the cup after extrusion by the action of an ejectoror knockout, such as that shown at D.

The dies having been properly formed, it is important that their surfaces be rendered extremely hard. I have found that a scleroscopic hardness (Shore test) of 90'or upward gives practically successful results.

The present invention provides a method by which a more homogeneous and erfect cup of zinc can be roduced than y the previous methods. uch cups are largely used as the zinc element in a dry battery, and for this purpose it is important that the molecular structure of the zinc be as uniform as possible. The drawing method heretofore used has required for its success a zinc of exceptional purity in its freedom from lead, cadmium, etc. and consequently a very expensive form of zinc. The drawn zinc batter shell has also been defective by reason of tie difference in or stalline structure set up in its walls by t 1e multiplicity of drawin operations; thus each time the shell is re uced in diameter by drawing, the effect is to create a zone extending around the shell havin a smaller grain structure than the meta intervening between that zone and the one created by the next subsequent reducing operation. causes a variation in the susceptibility of the metal to corrosion through contact with the chemicals of the battery. This disadvantage is wholly avoided by the present invention, which produces drawn cups or shells in a single operation, and with walls of uniform c stalline structure.

The extruding operation leaves the cup with a slightly irregular upper edge and the extruded cups are afterward trimmed to This condition a uniform height as shown for example by the line w-w in ig. 5.

What I claim is:- I

1. The process of working zinc which consists in subjecting a blank to pressure between male and female dies and extruding it through a contracted annular'space surrounding the male die in a. direction opposite to the movement of the male die, and while at a temperature approximating 150 degrees C.

2. The process of claim 1, the blank being of soft zinc practically free from grain for mation.

3. The process of claim 1, the blank being of zinc having a lead content not exceeding 0.6 per cent.

4. The process of claim 1, the blank being of zinc having a cadmium content not exceeding 0.5 per cent.

5. The process of claim 1, the blank being of zinc having a lead content not exceeding 0.6 per cent and a cadmium content not exceeding 0.5 per cent.

6. The process of working zinc, which consists in subjecting a blank to pressure within the cavity of a female die by forcing thereinto a male die of smaller diameter, and extruding it through an annular space between such dies in a direction opposite to the movement of the male die, and while at a temperature approximating 150 degrees C.

7 The process of working zinc which consists in subjecting a blank to pressure within the cavity of a female die by forcing thereinto a male die, having its largest diameter at its bottom portion, between which and the inner wall of the female die the zinc is extruded, and the male die diminished in diameter immediatel above such bottom portion torelieve tie extruded metal of pressure.

8. The process of working zinc which consists in subjecting a blank to presnre within the cavity of a female die by forcin thereinto a male die, having its largest diameter at its bottom portion, between which 6 and the inner wall of the female die the zinc is extruded, and the male die at its end conformed to the contour of the bottom of the cavityin the female die 81111 both relatively g shaped to im art a continuous outward flow to the meta between them duringextru- 10 slon.

In witness whereof, I have hereunto signed my name.

WALTER M.'TOWNE.- 

